[PATCH] Fix kernel NULL pointer dereference in xen-blkfront

[PATCH] Fix kernel NULL pointer dereference in xen-blkfront

[Kris Shannon]

When booting Xen Dom0 on a pre-release 3.2.1 hypervisor the system Oopses on a
"Unable to handle kernel NULL pointer dereference" in xenwatch.

>From the backtrace it looks like backend_changed is calling bdget_disk
with a NULL pointer.  Checking for NULL and returning ENODEV instead
allows the kernel to boot.
---
 drivers/block/xen-blkfront.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index f2fff5799ddf0fe1b41909b64d606d..3e2ab6d53adaeb70efa12f0a1f33bb 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -905,6 +905,8 @@ static void backend_changed(struct xenbus_device *dev,
 		break;

 	case XenbusStateClosing:
+		if (info->gd == NULL)
+			xenbus_dev_fatal(dev, -ENODEV, "gd is NULL");
 		bd = bdget_disk(info->gd, 0);
 		if (bd == NULL)
 			xenbus_dev_fatal(dev, -ENODEV, "bdget failed");
-- 
1.6.1.3

Re: [PATCH] Fix kernel NULL pointer dereference in xen-blkfront

[Jeremy Fitzhardinge]

Kris Shannon wrote:
> When booting Xen Dom0 on a pre-release 3.2.1 hypervisor the system Oopses on a
> "Unable to handle kernel NULL pointer dereference" in xenwatch.
>
> From the backtrace it looks like backend_changed is calling bdget_disk
> with a NULL pointer.  Checking for NULL and returning ENODEV instead
> allows the kernel to boot.
>   

Thanks, applied.  (BTW, please cc: me and xen-devel for Xen-related 
reports.)

Jens: could you pull this; I think this is probably -rc material.  This 
crash just started happening, so I guess its a side-effect of some core 
kernel change.

The following changes since commit c7241227f61ca6606a7fa3555391360d92bd8d9b:
  Jens Axboe (1):
        xen/blkfront: use blk_rq_map_sg to generate ring entries

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git xen/frontend/blkfront

Kris Shannon (1):
      Fix kernel NULL pointer dereference in xen-blkfront

 drivers/block/xen-blkfront.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)


Thanks,
    J

> ---
>  drivers/block/xen-blkfront.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index f2fff5799ddf0fe1b41909b64d606d..3e2ab6d53adaeb70efa12f0a1f33bb 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -905,6 +905,8 @@ static void backend_changed(struct xenbus_device *dev,
>  		break;
>
>  	case XenbusStateClosing:
> +		if (info->gd == NULL)
> +			xenbus_dev_fatal(dev, -ENODEV, "gd is NULL");
>  		bd = bdget_disk(info->gd, 0);
>  		if (bd == NULL)
>  			xenbus_dev_fatal(dev, -ENODEV, "bdget failed");
>   

Re: [PATCH] Fix kernel NULL pointer dereference in xen-blkfront

[Jens Axboe]

On Tue, Mar 03 2009, Jeremy Fitzhardinge wrote:
> Kris Shannon wrote:
>> When booting Xen Dom0 on a pre-release 3.2.1 hypervisor the system Oopses on a
>> "Unable to handle kernel NULL pointer dereference" in xenwatch.
>>
>> From the backtrace it looks like backend_changed is calling bdget_disk
>> with a NULL pointer.  Checking for NULL and returning ENODEV instead
>> allows the kernel to boot.
>>   
>
> Thanks, applied.  (BTW, please cc: me and xen-devel for Xen-related  
> reports.)
>
> Jens: could you pull this; I think this is probably -rc material.  This  
> crash just started happening, so I guess its a side-effect of some core  
> kernel change.
>
> The following changes since commit c7241227f61ca6606a7fa3555391360d92bd8d9b:
>  Jens Axboe (1):
>        xen/blkfront: use blk_rq_map_sg to generate ring entries
>
> are available in the git repository at:
>
>  git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git xen/frontend/blkfront
>
> Kris Shannon (1):
>      Fix kernel NULL pointer dereference in xen-blkfront
>
> drivers/block/xen-blkfront.c |    2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)

Sure, pulled.

-- 
Jens Axboe